1. Field of the Invention
This invention concerns a discharge-excited gas laser oscillator apparatus that uses preliminary UV ionization induced by corona discharges, and more particularly concerns an improved structure for the corona discharge and main discharge generator unit.
2. Description of the Related Art
The transversely excited atmospheric (TEA) laser performs laser oscillations by a method wherein, in forming the necessary inverted distribution region for laser oscillation, uniform glow discharges are generated in a gas at 1 atmosphere or higher pressure present in a main discharge space configured by a pair of opposing main electrodes. In such a TEA laser, in order to obtain uniform glow discharges throughout the gas in the main discharge space, it is necessary to subject all of the gas in the main discharge space to preliminary ionization prior to the commencement of the main discharges. With an excimer laser, in particular, the electrons in the rare gas used in the main discharges have a short life span, so that an inverse distribution is not formed unless the excitation is performed within that life span. Hence it is necessary to ionize as much of the entirety of the rare gas in the main discharge space as possible immediately prior to main discharge. There are currently a variety of methods used for the preliminary ionization, including X-rays, spark discharges, and corona discharges. Among these methods, however, those employing corona discharges are comparatively simple and contaminate the gas in the main discharge space only slightly, wherefore they are widely employed in capacity-migration preliminary ionization schemes.
In FIG. 11 is diagrammed an excimer laser apparatus which uses conventional corona preliminary ionization electrodes.
This excimer laser apparatus comprises a discharge generation unit equipped with a pair of main discharge electrodes 1 and 2 positioned in mutual opposition, a fan 8 that circulates laser gas G made up of Kr+Ne+F2, etc., in the direction of the arrow, and a heat exchanger 9 that cools the laser gas G.
In the discharge generator unit, a pair of corona preliminary ionization electrodes 12 are provided on the upper surface of a support plate 6, together with one of the main discharge electrodes 1, the corona preliminary ionization electrodes 12 being in opposition across gaps S1 and S2 of width W which extend in the longitudinal direction along either side, respectively, of the main discharge electrode 1. These gaps S1 and S2 are provided for the purpose of reducing the disparity in the distances between the preliminary ionization electrodes 12 and the main discharge electrodes 1 and 2, decreasing the difference between the preliminary ionization intensity in the discharge space in the vicinity of the one main discharge electrode 1 and the preliminary ionization intensity in the discharge space in the vicinity of the other main discharge electrode 2 to provide uniform preliminary ionization in the main discharge space, and thus stabilize the laser output.
The corona preliminary ionization electrodes 12 are configured such that columnar rear electrodes 4, respectively, are provided in the hollow interiors of cylindrical dielectric pipes 3, with the ends of corona electrodes 5 having L-shaped cross sections in contact with the outer surfaces of the dielectric pipes 3.
In such a configuration as this, first, before generating discharges with the main discharge electrodes 1 and 2, high voltages are applied between the rear electrodes 4 and the corona electrodes 5, thereby generating UV light by the corona discharges that are induced at the outer surfaces of the dielectric pipes 3, the starting points 11 thereof being the points of contact between the corona electrodes 5 and the dielectric pipes 3. The laser gas G with which the main discharge space is filled is preliminarily ionized by electrons that are generated by this UV light. Next, when high voltage is applied mutually between the pair of main discharge electrodes 1 and 2, the preliminarily ionized laser gas G exhibits dielectric breakdown, and the main discharge 7 starts. Also, the laser gas G is circulated by the gas flow created by the fan 8, so that the discharge products generated in the main discharge space by the previous discharge are carried away before the next discharge, thereby facilitating pulse oscillations at a high repetition frequency.
With the conventional laser apparatus described above, however, eddies Gxe2x80x2 of the laser gas G develop in the gaps S1 and S2 existing between the preliminary ionization electrodes 12 and the one main discharge electrode 1, causing metal fluorides, etc., produced by the corona discharges and main discharges, to be stagnated in the gaps S1 and S2. When these discharge products are again released into the main discharge space, the purity of the laser gas G deteriorates, and the main discharges 7 are destabilized, resulting in large fluctuation in laser output, which constitutes a problem.
With the foregoing in view, an object of the present invention is to provide a gas laser oscillator apparatus wherein laser gas flow is adjusted, thereby preventing discharge products from being stagnated and again released into the main discharge space, maintaining the purity of the laser gas in the discharge space, stabilizing the main discharges, and reducing fluctuation in laser outputs.
A first invention for attaining the object stated above is a gas laser oscillator apparatus comprising:
a first main discharge electrode and a second main discharge electrode positioned to face with each other;
a pair of preliminary ionization electrodes comprised of hollow dielectric pipes, rear electrodes placed in hollow interiors of said dielectric pipes, and corona electrodes positioned so as to be in contact with outer surfaces of said dielectric pipes, that are positioned at sides of said first main discharge electrode, among said first and second main discharge electrodes, so as to sandwich said first main discharge electrode therebetween, leaving prescribed gaps between said first main discharge electrode and themselves, respectively; and that generate corona discharges started at points of contact as starting points between said corona electrodes and said dielectric pipes, by application of a high voltage across said corona electrodes and said rear electrodes, so as to produce preliminary ionization in a main discharge space;
a support plate for securing and supporting said first main discharge electrode and said pair of preliminary ionization electrodes; and
laser gas that flows from a side of one of said preliminary ionization electrodes toward a side of other of the preliminary ionization electrodes through said main discharge space between said first and second main discharge electrodes;
said corona electrodes being positioned such that the starting points of said corona discharges on the surfaces of said dielectric pipes are lower than a height of a highest part of said first main discharge electrode, wherein:
objects are interposed in said gaps between said first main discharge electrode and said pair of preliminary ionization electrodes, from an upper surface of said support plate to the height of said starting points.
With such a configuration as this, by interposing the objects in the gaps between the first main discharge electrode and the pair of preliminary ionization electrodes, from the upper surface of the support plate to the height of the starting points, the generation of laser gas eddies in the gaps is suppressed, making it possible to prevent the retention in the gaps of discharge products produced by the corona discharges and main discharges.
When this configuration is implemented, there is no release of discharge products back into the laser gas in the main discharge space, and deterioration in laser gas purity can be prevented, wherefore the main discharges can be stabilized, so that, as a result, laser output fluctuation can be decreased.
A second invention is a gas laser oscillator apparatus comprising:
a first main discharge electrode and a second main discharge electrode positioned to face with each other;
a pair of preliminary ionization electrodes that are positioned at sides of said first main discharge electrode, among said first and second main discharge electrodes, so as to sandwich said first main discharge electrode therebetween, leaving prescribed gaps between said first main discharge electrode and themselves, respectively; and
a support plate for securing and supporting said first main discharge electrode and said pair of preliminary ionization electrodes; in which laser gas is made to flow from a side of one of said preliminary ionization electrodes toward a side of other of the preliminary ionization electrodes through a main discharge space between said first and second main discharge electrodes, wherein:
a through hole is formed in said first main discharge electrode, connecting one of said gaps with the other of said gaps.
With such a configuration as this, by forming a through hole in the first main discharge electrode so as to connect one of the preliminary ionization electrodes with the other, the laser gas is allowed to pass freely through this through hole, whereby the generation of laser gas eddies in the gaps is suppressed, making it possible to prevent the retention in the gaps of discharge products produced by the corona discharges and main discharges.
When this configuration is implemented, there is no release of discharge products back into the laser gas in the main discharge space, and deterioration in laser gas purity can be prevented, wherefore the main discharges can be stabilized, so that, as a result, laser output fluctuation can be minimized.
A third invention is a gas laser oscillator apparatus comprising:
a first main discharge electrode and a second main discharge electrode positioned to face with each other;
a pair of preliminary ionization electrodes that are positioned at sides of said first main discharge electrode, among said first and second main discharge electrodes, so as to sandwich said first main discharge electrode therebetween, leaving prescribed gaps between said first main discharge electrode and themselves, respectively; and
a support plate for securing and supporting said first main discharge electrode and said pair of preliminary ionization electrodes; in which laser gas is made to flow from a side of one of said preliminary ionization electrodes toward a side of other of the preliminary ionization electrodes through a main discharge space between said first and second main discharge electrodes, wherein:
through holes connecting a lower surface and an upper surface of said support plate are formed in said support plate in two regions where said gaps exist.
With such a configuration as this, by forming through holes in the support plate in the two regions where the gaps exist, so as to communicate from the lower surface to the upper surface of the support plate, the laser gas is allowed to pass freely through these through holes, whereby the generation of laser gas eddies in the gaps is suppressed, making it possible to prevent the retention in the gaps of discharge products produced by the corona discharges and main discharges.
When this configuration is implemented, there is no release of discharge products back into the laser gas in the main discharge space, and deterioration in laser gas purity can be prevented, wherefore the main discharges can be stabilized, so that, as a result, laser output fluctuation can be decreased.
A fourth invention is a gas laser oscillator apparatus comprising:
a first main discharge electrode and a second main discharge electrode positioned to face with each other;
a pair of preliminary ionization electrodes that are comprised of hollow dielectric pipes; rear electrodes placed in hollow interiors of said dielectric pipes; and corona electrodes positioned so as to be in contact with outer surfaces of said dielectric pipes, and that are positioned at sides of said first main discharge electrode, among said first and second main discharge electrodes, so as to sandwich said first main discharge electrode therebetween, leaving prescribed gaps between said first main discharge electrode and themselves, respectively; and
a support plate for securing and supporting said first main discharge electrode and said pair of preliminary ionization electrodes, in which laser gas is made to flow from a side of one of said preliminary ionization electrodes toward a side of other of said preliminary ionization electrodes through a main discharge space between said first and second main discharge electrodes, wherein:
conductors having heights lower than said first main discharge electrode are interposed in gaps between said first main discharge electrode and said preliminary ionization electrodes on an upper surface of said support plate; and
said corona electrodes are positioned relative to said dielectric pipes in a configuration wherein said dielectric pipes press against said conductors, so that said dielectric pipes, respectively, are held sandwiched between said conductors and said corona electrodes.
With such a configuration as this, by interposing conductors having heights lower than the first main discharge electrode in the gaps between the first main discharge electrode and the preliminary ionization electrodes, the generation of laser gas eddies in the gaps is suppressed, making it possible to prevent the retention in the gaps of discharge products produced by the corona discharges and main discharges.
When this configuration is implemented, there is no release of discharge products back into the laser gas in the main discharge space, and deterioration in laser gas purity can be prevented, wherefore the main discharges can be stabilized, so that, as a result, laser output fluctuation can be decreased.
If, moreover, the conductors and the corona electrodes are made to be in area contact with the outer surfaces of the dielectric pipes in a configuration wherein they cover the outer side surfaces of the dielectric pipes, respectively, almost all superfluously emitted light that does not contribute to laser oscillation is eliminated at the corona preliminary ionization electrodes, and almost the entire quantity of light emitted from the corona preliminary ionization electrodes is directed toward the main discharge space, wherefore it becomes possible to sharply improve laser oscillation efficiency.